This invention relates to a process for converting copper sulfide concentrates to anode copper. In one aspect, the invention relates to the conversion of copper matte to blister copper while in another aspect, the invention relates to a process which utilizes solidified copper matte to remove heat from and/or increase the throughput of a continuous, top-blown copper converting furnace.
U.S. Pat. Nos. 5,205,859 and 5,217,527, both to Goto, et al. and both incorporated herein by reference, describe a continuous process for converting copper concentrates to anode copper (the "Mitsubishi process"). The smelting apparatus used in the Mitsubishi process comprises (i) a smelting furnace for melting and oxidizing copper concentrates to produce a mixture of matte and slag, (ii) a separating furnace for separating the matte from the slag, (iii) a converting furnace for oxidizing the matte separated from the slag to produce blister copper, and (iv) a plurality of anode furnaces for refining the blister copper into anode copper. All of the furnaces are arranged in descending order with the smelting furnace at the highest elevation and the anode furnaces at the lowest elevation such that the processed copper is gravity transferred (i.e. cascades) in liquid or molten form from one to another through launders. In an alternative embodiment not described in these patents, one or more ladles are employed to transfer intermediate product (e.g. molten matte) from a lower elevation to a higher elevation to initiate the casacading effect over at least a part of the smelting process. Furthermore, the roof of each of the smelting and converting furnaces is fitted with a plurality of vertical lances through which one or more of copper concentrates (in the smelting furnace only), oxygen-enriched air, and flux are supplied to these furnaces.
The converting furnace is designed and positioned to receive a continuous flow of molten matte from the separation furnace. The converting furnace holds in its basin N (also known as a settler region) a bath of molten blister copper which was formed by the oxidation of molten copper matte that was fed earlier to the furnace. The bath typically comprises blister copper of about one meter in depth upon which floats a layer of slag of about 12 centimeters in thickness. As the liquid matte flows into the converting furnace, it spreads across the surface of the bath towards the lances and mixes with the blister copper forming an unstable molten matte phase (the bath does not contain a stable layer of molten copper matte). The high velocity oxygen-containing gas and flux from the lances penetrate through the slag and into the molten blister copper to form a foam/emulsion in which the molten copper matte is converted to molten blister copper. The newly-formed molten blister copper displaces existing molten blister copper out of the furnace, e.g. through tapholes, or a syphon, or a forehearth, etc., and the newly-formed slag flows toward a slag taphole for eventual removal from the furnace.
Since the oxidation of the iron and sulfur values in the molten matte is an exothermic reaction, considerable heat is generated within the converting furnace. Moderation and control of this heat, i.e. moderation and control of the temperature of the bath, particularly the temperature peaks, is important not only to the efficient operation of the furnace (and thus to the production of blister copper), but also to the life of the furnace refractory and other components. Prolonged periods of these temperature peaks, i.e. temperatures significantly in excess of the that required to the effect the reaction of molten matte (Cu--Fe--S) with oxygen (O.sub.2) and flux (e.g. CaO) to form copper metal (Cu.sup.0), molten slag (Cu.sub.2 O--CaO--Fe.sub.3 O.sub.4) and gaseous sulfur dioxide (SO.sub.2), can significantly shorten the life of the furnace refractory.
The temperature of the bath can be moderated by one of two methods. First, the amount of heat generated can be limited and second, the excess heat can be removed. Limiting the amount of heat generated requires controlling the amount and quality of reactants introduced into the bath. For example, one method of limiting the amount of heat generated is to introduce nitrogen into the furnace, thus reducing the level of oxygen enrichment. However, the addition of nitrogen reduces furnace throughput and depending on its manner of introduction, can increase bath turbulence. Moreover, controlling the quality of the reactants (e.g. the relative amounts of copper, iron and sulfur in the matte, etc.) is difficult at best due to the varying compositional nature of the starting materials, particularly the concentrate feed to the smelting furnace, and because the furnace is part of an continuous operation, any such measure has a ripple effect both up- and downstream.
Removing excess heat from the bath can be accomplished by a number of techniques two of which are heat transfer, e.g. by a cooling jacket and/or strategically placed cooling blocks, and by the introduction of a coolant, e.g. a material that absorbs heat upon its introduction into the bath (of which scrape anode copper and recycled converter slag are good examples). The addition of a coolant is practiced with both top-blown and other furnace designs, e.g. a Pierce-Smith converter as described in U.S. Pat. No. 5,215,571 to Marcuson, et al. However, the addition of copper scrap, particularly scrap copper anode, has it own set of problems not the least of which are sizing (e.g. shredding scrap copper anodes), introduction into the furnace (improper introduction can result in damage to the furnace), and the introduction of impurities into the molten blister copper, e.g. the noncopper values present in the coolant (which must ultimately be removed from the blister copper).